Welcome!
It's looks like your capable of a range of styles, and your work definitely shows promise.
However, I'm concerned that you might have a general tendency to leave out large shadow regions.
The best example might be your 'abbadan' rendition. It seems to rely solely on outlines to define his shape when there is a good opportunity to use shadows.
If we pick a light source above, we can create a strong contrast between his underbelly and say, his shoulders. The strong value changes work to differentiate the limbs and the gradual value changes can define the form.
Here's just a quick edit to show you what I'm talking about. Hope this helps.
